Method of treating and utilizing the black liquor obtained in the manufacture of soda and sulphate cellulose



the less soluble soda.

Patented Aug. 14, 1928.

UNITED S AT S PATENT orrica.

ERIK HKGGLUND,

or ABO, FINLAND.

mnon OI TREATING AN D UTILIZING THE BLACK LIQUOR OBTAINED IN THE MLNU- V l IACTUBIF OI SODA AND S'UIlZrPHA'Jl'E CELLULOSE.

Io Drawing. Application and June 18, 1927,

tained in the manufacture of soda or sulis first subjected to a suitable phate cellulose, heat and pressure treatment (at say 350 C. and 15()2O0 atm.) adapted to precipitate the chief quantity of the organic substances contained therein, in the form of carbonaceous and tarry matter, whereupon the solution discharged from the high pressure tank is treated for the purpose 0 extracting from it valuable organlc compounds and of converting the alkali contained therein into caustic form.

According to one method of carrying out the said prior process the acetate contained within the lye discharged from the high pressure tank is separated off by crystallization. To this end the liquor is rendered alkaline with a caustic alkali, which step is hereinafter referred to as causticization and is thereupon concentrated to cause the acetate contained in it to crystallize out. The mother liquor forming fresh white liqllior is returned to the boiler.

he causticization of the liquid coming from the high pressure tank does not, however, afford a sufficiently reliable means for l preventing the simultaneous precipitation of other sodium salts, for exam is in the form of soda. It may be advisab e, therefore, in certain conditions, to abandon. the direct method of extracting the acetate by crystallizing it out resort to a method,- which although less direct, yields acetate of a greater degree of purity. Accordin to the present invention this is done by rst evaporatin to dryness the sol1ition which is discharg from the high pressure tank, thereby'producing a residue containing acetate and soda, and thereiipon recovering the acetate by separating it from by fractional lixiviation of the resi e.

In order to increase further the degree of purity of the acetate, it is advisable to heat the dry residue (of the solution withdrawn bonized products after the causticization, and to Serial No. 199,873, and in Sweden June 21, 1926.

from the high pressure tank) before it is fractionally lixiviated, to such a degree that 1 whereas. the acetate remains undecomposed, the remainder of other organic com ounds present in the solution is decoinpose being artly carbonized and artly broken down into volatile compoun s. Substances produced by such heating are for example: formates, propionates and butyrates. been found suitable to heat to a temperature of about 300 C. 1

The fractional lixiviation gives a very pure acetate solution, which is separated from the solid residue which contains besides soda'. amongst other substances the carof decomposition of oranic compounds. The dry residue is subected to causticization' for the purpose of. recovering white liquor for opening up fresh quantities of wood, straw or the like; the carbonized products pass into the causticiza- Ption slime.

What I claim is 1. The method of treating and utilizing the black liquor obtained in the manufacture of soda and sulphate cellulose which consists in subjecting said liquor to a heat and pressure treatment adapted to precipitate the main ortion of organic substances therein as car onaceous an pitchy material, then separating the liquor from the precipitate, evaporating said liquor to dryness, sub1ecti'ng the dry residue to fractional lixiviation so as to obtain therefrom an acetate solution, separating said acetate solutionfrom the dry residue,-causticizin the residue and using the causticized resi no as causticizingvagent in white lye.

2. A' rocess as ,in-the ry residu'eis subjectedto a heating process before it is lixiv ated, said heating process adapted to decompose the remainder of organic substances present in the said residue besides the acetate. Y

In. testimony whereof, I have name to this specification at day of June, 1927.

- nan; Emmi),

signed in It has claimed in claim 1, wherelin this mi 

